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Digitized  by  the  Internet  Archive 

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University  of  Illinois  Urbana-Champaign 


http://archive.org/details/ooliteofstegenev55710lama 


STATE  OF  ILLINOIS 
DEPARTMENT  OF  REGISTRATION  AND  EDUCATION 

A.  M.  SHELTON,  'Director 

DIVISION  OF  THE 
STATE  GEOLOGICAL  SURVEY 

M.  M.  LEIGHTON.  Chief 
REPORT  OF  INVESTIGATIONS— NO.  10 

THE  OOLITE  OF  THE  STE.  GENEVIEVE  FORMATION 

BY 
J.  E.  LAMAR 


PRINTED  BY  AUTHORITY  OF  THE   STATE   OF  ILLINOIS 


URBANA,  ILLINOIS 
1926 


Reprinted  from  Transactions  of  the  Illinois  State  Academy  of  Science, 
Vol.  18,   1925 


STATE  OF  ILLINOIS 
DEPARTMENT  OF  REGISTRATION  AND  EDUCATION 

A.  M.  SHELTON,  Director 

DIVISION  OF  THE 
STATE  GEOLOGICAL  SURVEY 

M.  M.  LE1GHTON.  Chief 


Committee  of  the  Board  of   Natural    Resources 
and  Conservation 

A.  M.  Shelton,  Chairman 

Director  of  Registration  and  Education 

Kendbic  C.  Babcock 

Representing  the  President  of  the  Uni- 
versity of  Illinois 

Edson  S.  Bastin 
Geologist 


,  14      (48382      LOO      1-26) 


PAPERS  ON  GEOGRAPHY  AND  GEOLOGY        409 

THE  OOLITE  OF  THE  STE.  GENEVIEVE 
FORMATION1 

J.  E.  Lamar,  State  Geological.  Survey,  Urban  a 

The  term  oolite  is  derived  from  Greek  words  meaning 
egg-  and  rock,  and  was  suggested  by  the  resemblance  of 
a  mass  of  oolite  grains  to  the  roe  or  eggs  of  fish.  The 
word  oolite  is  used  to  describe  a  rock  made  up  of  oolite 
grains  to  which  the  term  spherules  or  spherites  is  ap- 
plied. A  spherule  is  denned  as  a  concretion,  commonly 
of  calcium  carbonate,  with  an  internal  radiating  and  con- 
centric structure.  The  central  nucleus  of  a  spherule  may 
be  a  foreign  particle  or  may  be  of  the  same  material 
as  the  oolite  grain  itself. 

ORIGIN   OF   OOLITE 

Two  different  modes  of  origin  have  been  assigned  to 
calcareous  oolite,  namely  organic  and  inorganic.  In  the 
former  case  the  oolite  grains  are  thought  to  have  resulted 
from  the  precipitation  of  calcium  carbonate  directly  or 
indirectly  by  bacteria  or  algae.  The  bacteria  or 
algae  may  have  formed  the  center  of  the  grain  or  have 
attached  themselves  to  a  foreign  body  which  became  the 
center  around  which  the  organisms  caused  a  precipita- 
tion of  calcium  carbonate. 

It  has  been  stated  that  calcareous  oolite  of  inorganic 
origin  has  been  formed  by  the  precipitation  of 
calcium  carbonate  around  minute  particles  of  sand 
or  other  foreign  bodies  kept  in  motion  so  that  all  sides 
might  become  about  equally  encrusted.  The  spherical 
shape  of  the  grains  is  supposed  to  have  been  due  to 
rolling  of  the  spherules  on  the  sea  bottom.  Somewhat 
in  contrast  to  this  idea  Bucher2  is  of  the  opinion  that 
most  oolitic  grains  were  formed  from  a  dispersion 
medium  "by  at  least  one  constituent  substance  changing 
from  the  emulsoid  state  to  that  of  a  solid"  and  that  "the 
spherical  shape  of  the  grains  is  due  to  the  tendency  of 
the  droplets  forming  during  this  process  of  separation 
to  coalesce. ' '  Further  he  ascribes  the  difference  between 
the  radial  and  concentric  structure  as  depending  "on 

'Published  by  courtesy  of  the  Chief,  Illinois  State  Geological  Survey. 
2Bucher,   W.   H.,   On   oolites  and   spherulites.   Jour.   Geol.   V.   2(i,    1918,   p.   602. 


410  ILLINOIS  STATE  ACADEMY  OF  SCIENCE 

the  amount  of  other  substance  thrown  out  simultaneously 
with  and  mechanically  enmeshed  in  the  growing 
structure. ' ' 

In  either  of  the  cases  mentioned  in  the  above  para- 
graph it  would  seem  possible  that  organic  remains  might 
be  trapped  within  oolite  grains  during  their  formation 
without  actually  playing  a  primary  part  in  their 
development  or  growth. 

THE  STE.   GENEVIEVE   OOLITE 

The  Ste.  Genevieve  is  the  uppermost  formation  of  the 
lower  Mississippian  system.  It  is  exposed  in  the  south- 
ern and  western  parts  of  Illinois  and  is,  in  o-cneral,  a  very 
pure  limestone.  The  lithologic  character  of  the  forma- 
tion varies  both  horizontally  and  vertically,  but  the 
presence  of  conspicuous  beds  of  oolite  is  one  feature 
which  is  widespread  and  constant.  Locally  this  oolite 
is  cross-bedded.  The  spherules  vary  from  a  fraction  of 
a  millimeter  to  a  maximum  of  about  2  millimeters  in 
diameter,  and  are  composed  dominantly  of  calcium 
carbonate.  Included  with  the  calcium  carbonate  are 
small  amounts  of  disseminated  organic  and  argillaceous 
material.  None  of  the  sections  of  Ste.  Genevieve  oolite 
examined  suggested  an  organic  origin  of  the  spherules 
and  they  are  therefore  thought  to  have  been  formed  by 


TYPES  OF  SPHERULES  FOUND  IN  THE  STE.  GENEVIEVE 
FORMATION 

The  Ste.  Genevieve  oolite  contains  spherules  in  many 
different  stages  of  development,  and  it  is  difficult  to  di- 
vide the  forms  into  groups  which  will  have  a  sharp  line  of 
demarcation.  It  is  possible,  however,  to  recognize  three 
distinctly  different  types  of  spherules  as  follows:  (1) 
those  with  an  angular  central  grain,  (2)  those  with  a 
rounded  central  grain,  and  (3)  those  which  show  no 
distinct  central  grain. 

The  first  type  of  spherule  with  an  angular  central  grain 
is  illustrated  by  the  spherule  near  the  center  of  Fig.  1  and 
by  Fig.  2.  In  some  spherules  the  central  grains  are  sur- 
rounded by  but   one  ring  of  calcium  carbonate,  but  in 


Fig.  1.      Drawing  of  etched  polished  surface  of  oolite.     Magnified  about  50  times. 


Fig.  2.  Drawing  of  thin  section  i>l'  spherule  of  type  1.     Magnified  about  125  times. 


Fig.  3.     Drawing  of  thin  section  of  spherule  of  type  3.  Magnified  about  125  times 


V- 


Fig.  4.     Drawing  of  thin  section  of  spherule  of  type  •'!.    Magnified  about  120  times. 


Fig.  5.     Drawing  of  thin  section  of  oolite.     Magnified  al>out  50  times. 


PAPERS  ON  GEOGRAPHY  AND  GEOLOGY        411 

many  four  or  five  concentric  deposits  are  present.  As 
many  as  eight  rings  have  been  observed.  A  radiating 
structure  is  commonly  present  in  the  material  composing 
the  rings. 

The  second  type  of  spherule  with  a  rounded  center  is 
illustrated  by  four  of  the  forms  shown  in  Fig.  1.  In  many 
the  centers  are  almost  spherical  but  more  commonly  they 
are  ovoid  and  somewhat  elongated.  A  maximum  of  nine 
concentric  deposits  of  calcium  carbonate  have  been  noted 
around  rounded  central  grains  and  in  general  a  radiating 
structure  is  exhibited  by  the  material  composing  the 
rings. 

The  third  type  of  spherule,  characterized  by  the  lack 
of  a  distinct  central  grain,  is  shown  in  Figs.  3  and  4. 
Figure  3  shows  a  form  with  the  concentric  and  radiating 
structure  well  developed  and  Fig.  4  a  spherule  in  which 
there  is  but  a  slight  suggestion  of  these  structures.  There 
are  all  gradations  between  these  two  sorts  of  spherules. 
Eleven  distinct  rings  were  noted  in  a  spherule  of  this 
type  and  in  general  they  are  the  more  annular  of  the 
types  described. 

THE    CENTRAL   GRAINS 

There  are  two  classes  of  central  grains  which  may  be 
recognized.  The  first  is  illustrated  in  Fig.  5,  and  is 
thought  to  have  been  formed  by  the  recrystallization  of 
the  calcium  carbonate  forming  the  amorphous  centers  of 
spherules  of  the  third  type  such  as  is  shown  in  Fig.  3. 
During  the  recrystallization,  the  argillaceous  or  organic 
material  included  in  the  original  center  was  excluded 
from  the  growing  crystalline  center  and  formed  the  con- 
spicuous dark  ring  around  the  central  grain  as  shown  in 
Fig.  5.  These  grains  were  slightly  more  rapidly  soluble 
in  hydrochloric  acid  than  the  concentric  deposits  about 
them.  In  the  case  of  the  central  grain  of  Fig.  2,  it  may 
have  been  formed  in  the  same  manner  as  the  preceding, 
but  the  absence  of  the  dark  band  around  the  center  sug- 
gests that  either  the  primary  amorphous  center  was  very 
pure  or  else  the  spherule  has  resulted  from  the  accretion 
of  calcium  carbonate  around  an  angular  calcite  grain. 

The  second  class  of  central  grains  is  shown  in  Fig.  1, 
which  is  an  enlarged  sketch  made  from  a  photomicro- 


412  ILLINOIS  STATE  ACADEMY  OF  SCIENCE 

graph  of  a  piece  of  oolite  with  a  polished  surface  which 
was  etched  with  hydrochloric  acid.  This  etching  resulted 
in  a  more  rapid  solution  of  the  material  surrounding  the 
central  grains  than  of  the  grains  themselves,  thus  leaving 
the  centers  standing  as  slight  projections  above  the  gen- 
eral level  of  the  smoothed  surface.  The  centers  are  com- 
posed of  calcium  carbonate  and  also  the  rings  surround- 
ing them,  for  the  specimen  was  entirely  soluble  in  acid 
with  but  a  very  slight  residue.  The  Ste.  Genevieve  forma- 
tion is  in  parts  made  up  entirely  of  more  or  less  rounded 
detrital  particles  and  fragments  of  shells  and  tests,  some 
of  which  still  exhibit  recognizable  structures,  and  the 
second  type  of  centers  are  thought  to  be  such  fragments. 
In  some  oolites  recognizable  shell  and  bryozoa  fragments 
have  been  noted  as  spherule  centers.  The  calcium  carbon- 
ate forming  the  concentric  deposits  around  these  centers 
may  possibly  collect  around  them  in  the  manner  sug- 
gested under  the  first  mentioned  mode  of  formation  of 
oolitic  grains. 

SUGGESTIONS    AS    TO    CONDITIONS    OF    SEDIMENTATION    DURING 
THE    FORMATION    OF    STE.    GENEVIEVE    OOLITE 

One  of  the  outstanding  features  which  a  study  of  the 
limestones  of  the  Ste.  Genevieve  formation  brings  out  is 
the  large  amount  of  detrital  calcareous  material  which  is 
associated  with  the  oolite  of  the  formation  or  is  present 
in  beds  in  which  oolitic  grains  are  essentially  missing  or 
uncommon.  A  great  deal  of  this  detritus  is  doubtless 
derived  from  the  comminution  of  calcareous  tests.  A 
part  of  it,  however,  may  have  been  obtained  from  lime- 
stone adjacent  to  the  site  of  deposition  subject  to  active 
erosion  with  comparatively  small  amount  of  transporta- 
tion. This  is  suggested  by  what  appear  in  thin  sections 
to  be  fragments  of  limestone.  One  was  noted  which  con- 
tained within  it  two  well  formed  spherules  and  a  form 
suggestive  of  a  fragment  of  a  crinoid  stem.  The  associ- 
ation of  oolite  grains  and  calcareous  detritus,  the  pres- 
ence of  fragments  of  limestone,  taken  together  with  the 
cross-bedding  found  in  places  in  the  Ste.  Genevieve 
formation,  suggest  comparatively  shallow  water  condi- 
tions, where  erosion  and  transportation  were  relatively 


PAPERS  ON  GEOGRAPHY  AND  GEOLOGY        413 

active.  The  question  is  raised  as  to  whether  the  spherules 
as  found  have  been  formed  in  situ  or  whether  in 
the  deeper  waters  somewhat  distant  from  the  shore, 
there  may  not  have  been  an  oolite-forming  zone  where 
spherules  were  constantly  forming,  to  be  carried  shore- 
ward during  storms  and  rough  water,  there  to  be  com- 
mingled with  the  calcareous  sands  of  the  sea  beaches, 
bars,  and  shore.  The  thin  section  from  which  Fig.  5  is 
drawn  contains  no  calcareous  debris  other  than  a  few 
gastropod  shells  which  show  very  little  evidence  of  ero- 
sion or  abrasion.  This  absence  of  debris  and  the  develop- 
ment of  projections  from  the  outer  concentric  bands  of 
the  spherules  suggest  conditions  favoring  uninterrupted 
growth  of  the  spherules.  This  section  may,  therefore, 
represent  the  deposits  of  primary  oolite  of  the  oolite- 
forming  zone. 

In  contrast  with  the  preceding  suggestion  that  oolite 
may  be  formed  in  off  shore  zones,  it  may  be  pointed  out 
that  a  beach  subject  to  tidal  inundation  and  subsequent 
withdrawal  might  well  offer  a  favorable  site  for  the  ac- 
cumulation of  calcium  carbonate  around  sand  grains,  both 
calcareous  and  siliceous.  The  re-working  of  such  a  de- 
posit by  contemporaneous  or  later  currents  without  much 
abrasion  may  account  for  the  varied  occurrences  of  the 
spherules. 


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